1. Technical Field
The present invention relates to nanoscale fabrication and, more particularly, to fabrication of structures using sidewall image transfer.
2. Description of the Related Art
In conventional sidewall image transfer (SIT), sidewalls are formed around a structure. The structure is then removed, leaving only the sidewalls. The sidewalls are used to block an etch, resulting in relatively small feature sizes. Toward this end, SIT can be performed multiple times, shrinking the feature size with each iteration.
However, while performing multiple SIT iterations is effective at producing structures with regular spacing, it is challenging to integrate such processes with regions that have variable spacing. In one example, a dense fin pitch of less than about 40 nm may be desired, where this is less than one half of the lithographic limit. To form such dense fin structures, the SIT process may be applied twice. At the same time, for example in a static random access memory (SRAM) area, variable fin spacing, with fin pitch less than the lithography limit but larger than ½ of the lithography limit, may be desired to achieve high SRAM cell density. Because of the lithographic limits in this example, single fin trimming at 40 nm would not be doable, and there is no method to integrate the double SIT regions with variable fin spacing regions.